“Sheep” and “sharp” are not a million miles apart in phonological terms, but they not nearly as close as Schafe and scharfe. In addition, while I’ve translated the German so that the noun and verb are both “shears,” this renders it a bit awkward and not really the sort of awkward that renders it funnier. So perhaps it would be closer to the feel of the original to say: “To spear sharks you need sharp spears?!”